Agreed, and I would add that there must be a formal motion to exclude the public, passed by the council, and it must give a satisfactory reason for the conclusion. Although, obviously, the reason does not need to be so specific as to give away confidential information. I'd add to the list above the requirement to exclude the public in cases where otherwise the council would breach a duty of confidentiality, but this must be a formal obligation to be relevant, not just a wish for secrecy. It is fundamental to open democracy that council meetings are held in public whenever possible.